(d) When DS3 lights, both the developer and dryer have reached the
temperature band. The dryer temperature at this point is automatically set back from
the set point temperature. The temperature controller maintains proper temperatures by
alternately switching power to the heaters. You will observe DS1 and DS2 blinking at a
50:50 ratio or less when there is no film in the processor.
(e) When you load film into the processor, more heat is available to the
dryer to bring it to set point temperature. Leds DS1 and DS2 show a proportion of up to
20:80 for the first sheet of film, which varies depending on the operating load. More
heat becomes available to the dryer by a setback circuit. The circuit runs from a signal
on J2 (DS2 lights), activated by the film switch. The setback circuit has the effect of
increasing the dryer temperature dial setting by changing the resistance of the dial and
temperature probe input to the temperature controller.
(f) The flow chart in figure 1-20 gives a procedure for checking a no
heat condition. Diagnose other heating problems in the same way. The leds on PC
board J3 indicate whether or not the controller circuit is functioning. If these leds are
working, the problem is probably not in the PC board. A quick way to check if the PC
board is working is to turn up one temperature dial and turn down the other. You should
see DS1 or DS2 light. If neither of the leds light, perform the power supply and fuse
check in section 1-4c(1)(a)-(d). Replace the PC board J3 if the power supply is good.
Perform temperature calibration in Lesson 3, Perform Calibration/Verification on X-ray
Film Processors, after installing a new PC board.
(g) Shorting causes constant power to the heating element, therefore
constant heat, resulting in high developer activity or evaporation. Since the developer
heater has a safety thermostat, a shorted triac may cause overheating, cut off until the
element cools down, then cause overheating again. This shows as erratic temperature
control. A shorted dryer heater triac causes overheating, which will trip the dryer
thermostat. If the thermostat trips again after you push the reset button, the problem is
probably due to a shorted triac. A faulty temperature probe can also cause erratic
(h) You check power to the developer heater at terminal strip TS6.
Turn OFF the power switch and turn up the developer temperature dial. Turn the power
switch ON again, so that DS1 on the PC board J3 lights. Check for line voltage
between TS6-6 and TS6-19, when SD1 is lit. Turn down the temperature dial and
check for no voltage, when DS1 is not lit. If there is voltage at TS6 when DS1 is not lit,
then triac CR1 is shorted and you must replace it.
(i) The developer heater has a safety thermostat (TH3) that
automatically resets after it cools down (figure 1-21). The cutoff point is approximately
130F. A shorted triac can cause fluctuating developer temperature and results in the
heater heating up, cutting off and cooling down, and then heating up again. The voltage
between TS6-6 and TS6-19 is line voltage. If there is no voltage on a hot heater,
thermostat TS3 may have cut out. Wait for it to cool off and recheck the voltage.